1. Field of the Invention
This invention relates to a driving apparatus for doors applied to windows, walls, opening portions as doorways of houses or vehicles, and the like, and more particularly to an automatic linear-motor-type driving apparatus.
2. Description of the Prior Art
As a linear-motor-type driving apparatus as described above, a driving apparatus having a cylindrical linear motor which is disclosed on page 136 in "Linear Motor Handbook" published by Kogyo Chosakai Publishing Co., Ltd., is conventionally used. The conventional driving apparatus is installed the top of doors, as described in FIG. 5 of the present patent application drawings. This apparatus has a round bar 1 as a secondary member of a linear motor, a cylindrical body 2 through which the bar 1 is slidably inserted. The cylindrical body 2 contains a primary coil therein and constitutes the linear motor with the rod 1. Denoted 3 is a door, which is supported on a rail 5 by rollers 4 disposed on the top of the door 3. On applying power to the cylindrical body 2, the rod 1 and the cylindrical body 2 work as a linear motor so that the cylindrical body 2 slides along the rod 1 to open and close the door 3 along the rail 5.
However, the prior art described above has following drawbacks.
In the prior art, two guide members, the rod 1 and the rail 5, are used to guide the door 3, which makes the structure of the driving apparatus complicated. Further, it is difficult to adjust parallelism between the two guide members.
When the rail 5 is not used to support the door 3 but only the rod is used to directly support the weight of the door 3, the wear of the rod 1 on the surface thereof will considerably be added due to sliding movement under heavy load. As a result, the gap between the surface of the rod 1 as a secondary member of the linear motor and the primary coil increases faster than usual, which hastens the malfunction of the linear motor.
In order to increase thrust force for opening and closing the door 3, the cylindrical body and the primary coil must be lengthened. However, the length of the cylindrical body 2 may be restricted due to the width of the door 3, which may prevent the thrust force from being increased.